The present invention relates to allowed U.S. patent application Ser. No. 08/965,495, to the lubrication of surfaces that require lubrication in a refrigeration chiller when the chiller is in operation and/or to the cooling, by system refrigerant, of the motor by which the compressor of such a chiller is driven. In its preferred embodiment, the present invention relates to combined oil and refrigerant pump apparatus that ensures the delivery, under all operating conditions, of both lubricant and liquid refrigerant to the locations at which they are needed in a refrigeration chiller that employs a low pressure refrigerant.
Refrigeration chiller components include a compressor, a condenser, a metering device and an evaporator, the compressor compressing a refrigerant gas and delivering it, at relatively high pressure and temperature, to the chiller's condenser. The relatively high pressure, gaseous refrigerant delivered to the condenser rejects much of its heat content and condenses to liquid form in a heat exchange relationship with a heat exchange medium flowing therethrough.
Condensed, cooled liquid refrigerant next passes from the condenser to and through the metering device which reduces the pressure of the refrigerant and further cools it by a process of expansion. Such relatively cool refrigerant is then delivered to the system evaporator where it is heated and vaporizes in a heat exchange relationship with a liquid, such as water, flowing therethrough. The vaporized refrigerant then returns to the compressor and the liquid which has been cooled or "chilled" in the evaporator flows to a heat load in a building or in an industrial process application that requires cooling.
The compressor portion of a chiller typically includes both a compressor and a motor by which the compressor is driven. Such motors, in most if not all chiller applications, require cooling in operation and have often, in the past, been cooled by system refrigerant. In many chiller designs, gaseous refrigerant has been sourced upstream or downstream of the compressor for such purposes. In other designs, compressor drive motors have been cooled by liquid refrigerant sourced from a location within the chiller.
Chiller compressor drive motor cooling arrangements and chiller lubrication systems have, historically, been discrete from each other. In many cases, however, operation of the systems by which lubricant and motor cooling fluid were delivered to the locations of their use was predicated on the existence of a sufficiently high differential pressure within the chiller by which to drive oil or refrigerant from a relatively higher pressure source location to the relatively lower pressure location of their use in the chiller for such purposes.
The chemical constituencies and operating characteristics of refrigerants used in chillers have changed over the years, primarily as a result of environmental considerations, and the use of so-called "low pressure" refrigerants, such as HCFC 123, has become common in the past decade. These refrigerants are such that under certain chiller operating conditions the temperature and pressure existing in the system condenser approach those existing in the evaporator. As such, a sufficiently high pressure differential between the system evaporator and system condenser cannot be counted upon to exist under all chiller operating conditions to ensure the continuous availability of a pressure that can reliably be used to drive oil from the chiller's oil supply tank to chiller surfaces that require lubrication. Nor can such a reliably high pressure differential be counted upon to exist to ensure the delivery of refrigerant from a first chiller location to the motor which drives the system's compressor for purposes of cooling that motor. Both, once again, were common past practices that were permitted by the use of "higher pressure" refrigerants than are used today. In some applications, such practices continue to be in use today.
In view of the above-described circumstances, the present invention seeks, in its preferred embodiment, to advantageously incorporate aspects of both the lubrication system and motor cooling system in a refrigeration chiller in which a low pressure refrigerant is used to ensure, under all chiller operating conditions, the delivery of lubricant and refrigerant to the locations of their use for lubrication and motor cooling purposes. A second embodiment, relating to the pumping of liquid refrigerant independent of any relationship with the pumping of oil, is also described.